The primitive telephone has been greatly improved, the double electro-magnet being replaced by a single bar magnet having a small coil or bobbin of fine wire surrounding one pole, in front of which a thin disc of ferrotype is fixed in a circular mouthpiece, and serves as a combined membrane and armature. On speaking into the mouthpiece, the iron diaphragm vibrates with the voice in the magnetic field of the pole, and thereby excites the undulatory currents in the coil, which, after travelling through the wire to the distant place, are received in an identical apparatus. [This form was patented January 30, 1877.] In traversing the coil of the latter they reinforce or weaken the magnetism of the pole, and thus make the disc armature vibrate so as to give out a mimesis of the original voice. The sounds are small and elfin, a minim of speech, and only to be heard when the ear is close to the mouthpiece, but they are remarkably distinct, and, in spite of a disguising twang, due to the fundamental note of the disc itself, it is easy to recognise the speaker. This later form was publicly exhibited on May 4, 1877 at a lecture given by Professor Bell in the Boston Music Hall. 'Going to the small telephone box with its slender wire attachments,' says a report, 'Mr. Bell coolly asked, as though addressing some one in an adjoining room, "Mr. Watson, are you ready!" Mr. Watson, five miles away in Somerville, promptly answered in the affirmative, and soon was heard a voice singing "America."....Going to another instrument, connected by wire with Providence, forty-three miles distant, Mr. Bell listened a moment, and said, "Signor Brignolli, who is assisting at a concert in Providence Music Hall, will now sing for us." In a moment the cadence of the tenor's voice rose and fell, the sound being faint, sometimes lost, and then again audible. Later, a cornet solo played in Somerville was very distinctly heard. Still later, a three-part song floated over the wire from the Somerville terminus, and Mr. Bell amused his audience exceedingly by exclaiming, "I will switch off the song from one part of the room to another, so that all can hear." At a subsequent lecture in Salem, Massachusetts, communication was established with Boston, eighteen miles distant, and Mr. Watson at the latter place sang "Auld Lang Syne," the National Anthem, and "Hail Columbia," while the audience at Salem joined in the chorus.' Bell had overcome the difficulty which baffled Reis, and succeeded in making the undulations of the current fit the vibrations of the voice as a glove will fit the hand. But the articulation, though distinct, was feeble, and it remained for Edison, by inventing the carbon transmitter, and Hughes, by discovering the microphone, to render the telephone the useful and widespread apparatus which we see it now.